Shouldn't it be: ^\.{3}(\..{3}){3}$ because you want to match "..." followed by "\..." 3 times?

However, something like ^(\.?.{3}){4}$ would also match "..." repeated 4 times, e.g. "abcabcabcabc"? Unless I just misunderstood the question.

You can use the regex ^(.?[^\n]{3}){4}$.

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Shouldn't ruby code be using 'match?' instead of 'match'

/^(...\.?){4}$/